Re: [RFC/PATCH 4/5] completion: get rid of compgen

> On Sat, Nov 17, 2012 at 3:12 PM, SZEDER Gábor <szeder@ira.uka.de> wrote:
>> On Sat, Nov 17, 2012 at 12:42:38PM +0100, Felipe Contreras wrote:
>>> On Sat, Nov 17, 2012 at 12:00 PM, SZEDER Gábor <szeder@ira.uka.de> wrote:
>>> > On Sat, Nov 17, 2012 at 02:38:17AM +0100, Felipe Contreras wrote:
>>> >> The functionality we use is very simple, plus, this fixes a known
>>> >> breakage 'complete tree filename with metacharacters'.
>>> >>
>>> >> Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
>>> >> ---
>>> >>  contrib/completion/git-completion.bash | 6 +++++-
>>> >>  1 file changed, 5 insertions(+), 1 deletion(-)
>>> >>
>>> >> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
>>> >> index 975ae13..ad3e1fe 100644
>>> >> --- a/contrib/completion/git-completion.bash
>>> >> +++ b/contrib/completion/git-completion.bash
>>> >> @@ -227,7 +227,11 @@ fi
>>> >>
>>> >>  __gitcompadd ()
>>> >>  {
>>> >> -     COMPREPLY=($(compgen -W "$1" -P "$2" -S "$4" -- "$3"))
>>> >> +     for x in $1; do
>>> >> +             if [[ "$x" = "$3"* ]]; then
>>> >> +                     COMPREPLY+=("$2$x$4")
>>> >> +             fi
>>> >> +     done
>>> >
>>> > The whole point of creating __gitcomp_nl() back then was to fill
>>> > COMPREPLY without iterating through all words in the wordlist, making
>>> > completion faster for large number of words, e.g. a lot of refs, or
>>> > later a lot of symbols for 'git grep' in a larger project.
>>> >
>>> > The loop here kills that optimization.
>>>
>>> So your solution is to move the loop to awk? I fail to see how that
>>> could bring more optimization, specially since it includes an extra
>>> fork now.
>>
>> This patch didn't aim for more optimization, but it was definitely a
>> goal not to waste what we gained by creating __gitcomp_nl() in
>> a31e6262 (completion: optimize refs completion, 2011-10-15).  However,
>> as it turns out the new version with awk is actually faster than
>> current master with compgen:
>>
>>   Before:
>>
>>     $ refs="$(for i in {0..9999} ; do echo branch$i ; done)"
>>     $ time __gitcomp_nl "$refs"
>>
>>     real    0m0.242s
>>     user    0m0.220s
>>     sys     0m0.028s
>>
>>   After:
>>
>>     $ time __gitcomp_nl "$refs"
>>
>>     real    0m0.109s
>>     user    0m0.096s
>>     sys     0m0.012s
>
> This one is even faster:
>
> while read -r x; do
>         if [[ "$x" == "$3"* ]]; then
>                 COMPREPLY+=("$2$x$4")
>         fi
> done <<< $1
>
> == 10000 ==
> one:
> real    0m0.148s
> user    0m0.134s
> sys     0m0.025s
> two:
> real    0m0.055s
> user    0m0.054s
> sys     0m0.000s